The experiments are aimed at a better understanding of: 1) Brain stem sites and transmitters involved in nociception and antinociception; 2) morphine's interaction with transmitters at extra hypothalamic sites for the secretion of luteinizing hormone; and 3) the role played by substance P in nociception and antinociception. The experiments employ: intracerebral drug microinjections; electrophysiologic/microiontophoretic drug evaluations, and assays for tissue contents of serotonin, norepinephrine, substance P and luteinizing hormone.